[unreadable] The significant advances in understanding the role of genetic abnormalities in tumor initiation, progression, and metastasis raises the promise of gene therapy for solid tumors. Delivery of genes to tumor mass for the purpose of efficient intracellular uptake and protein expression remains a formidable challenge. The proposed study focuses on the formulation, using specific design criteria, of DNA delivery systems for solid tumor targeting and subsequent cellular uptake, trafficking, and nuclear entry for efficient expression. Plasmid DNA-containing long-circulating nanoparticle formulations will be made with natural and synthetic biodegradable cationic polymers. When administered in the systemic circulation, long-circulating poly (ethylene glycol)-grafted (PEGylated) gelatin and poly (ethylene oxide) (PEO)-modified poly (beta-amino ester) nanoparticles will be taken up by the tumor mass due to the enhanced permeability and retention effect and internalized in tumor cells by non-specific endocytosis. These carrier systems will release DNA in the low pH and hypoxic environment of the tumor. Upon cell uptake, encapsulated plasmid DNA is expected to be released efficiently from the endosome and remain stable for optimum transfection. Our preliminary studies show that these nanoparticle formulations can be used for DNA encapsulation, were efficiently internalized by the tumor cells, and resulted in transfection of the encoded protein. The specific aims of our study are: (1) to formulate and optimize DNA-containing long-circulating nanoparticles, (2) to study cell uptake, trafficking, and transfection in vitro in Lewis lung carcinoma, B16 melanoma, and EMT-6 mammary tumor cells lines, (3) to examine the disposition and transfection efficiency in mice. The results of this study will provide valuable information on the development of safe and efficacious nonviral vectors for in vivo DNA delivery specifically to solid tumor. [unreadable] [unreadable]